People say that Rubio will run for Governor of Florida if he doesn't become the monimee. Of course, the question is whether or not Rubio could be elected Governor of Florida. He'd be running for an office after leaving an office to run for President from and lose. Could he win a Republican primary? There are other Republicans who want to be Governor, most notably FL Attorney General Pam Bondi, who has won statewide twice. Why should she step aside for Rubio, especially when she's term limited? Why would Republican voters view Rubio as someone deserving? How would Rubio be viewed by independents after running a failed Presidential campaign? And how would Florida's GOP (and the national GOP, for that matter) would view Rubio if, after giving up his seat for a failed Presidential run, Democrat Patrick Murphy wins Rubio's Senate seat?
If Rubio fails to become the nominee, he needs to immediately get some kind of high-profile Cabinet level position. Even Ambassador to the UN would suffice. If it's Trump that gets elected and Trump shuts out Rubio, he should try to become RNC Chairman. Short of that, he'll become a has-been.
Remember that Bill Nelson's seat is going to be in election in 2018... Rubio can broke a deal to get free-run in gubernatorial race.
But why would Florida be inclined to give him another go in the Senate? He's already said he doesn't want to be there, and disrespected the office by not showing up.